1. Field
This disclosure relates to wireless communications and, more particularly, to improving data transmission rates.
2. Description of Related Art
In a wireless communication system operating according to the Telecommunication Industry Association IS-856 standard (commonly referred to as Evolution-Data Only, or “EV-DO”) or the like, the data rate received by a mobile station (or “access terminal”) on the forward link is proportional to the signal-to-noise ratio (C/I) of the pilot signal received by the mobile station on the forward link. In particular, IS-856 defines a set of correlations between C/I ratios and data rates, such that, the higher the C/I ratio, the higher the data rate, and the lower the C/I ratio, the lower the data rate. Further, IS-856 dictates that a mobile station should measure a C/I ratio associated with a base station communication sector that is serving the mobile station and then request the base station to transmit on the forward link at the data rate corresponding to that measured C/I. (Generally, the base station will then transmit at that requested data rate, although the actual data rate may vary somewhat, depending on factors such as actual traffic load at the time.) The IS-856 standard is incorporated by reference herein in its entirety.
Additionally, under IS-856, each sector has an allocated power level (i.e., its power amplifier (PA) is set to output at a particular sector power level), and the sector transmits its pilot signal at a certain percentage (typically a high percentage) of the sector's total allocated power. Thus, the pilot signal in each sector is largely a fixed power level, based on the power generally allocated to the sector. Since the data rate on the IS-856 forward link is proportional to the signal-to-noise ratio, it follows that a mobile station will operate at (or at least request operation at) a lower data rate when more noise is present in the sector.
One factor that adds to the noise in an IS-856 sector is “pilot pollution”, e.g., interference from pilot signals of other sectors. This phenomenon typically occurs at border areas, where sectors overlap. Under IS-856, a mobile station operates on just one sector at a time, usually the sector having the highest C/I detected by the mobile station. If the mobile station detects other pilots at the same time and interference results, such interference will increase the denominator, I, of the serving sector's C/I ratio. This will result in a decrease in the C/I ratio and a corresponding decrease in the forward link data rate (or at least the requested forward link data rate).
Another factor that reduces the C/I ratio associated with a serving sector is the distance the mobile station is from the serving sector. As the mobile travels away from a serving sector, the pilot signal (and data signals) will become more attenuated (in addition to interference from pilot signals from neighboring cell sectors). This attenuation will reduce the numerator, C, of the serving sector's C/I ratio and, thus, also result in a reduction in the requested forward link data rate.
Based on the foregoing, alternative approaches for communicating forward link data to improve overall data transmission rates are desirable.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.